The term may be a derivation of the nickname of Asa Brainard, (real first name: "Asahel"), a 19th-century star pitcher, who was sometimes referred to as "Ace".[1][2]

In the early days of baseball, the term "ace" was used to refer to a run.[3]

A lot of modern baseball analysts and fans have started using the term "ace" to refer to the elite pitchers in the game, not necessarily to the best starting pitcher on each team.[4] For example, the April 27, 1981 Sports Illustrated cover was captioned "The Amazing A's and Their Five Aces" to describe the starting rotation of the 1981 Oakland Athletics.[5]